I. Field of the Invention
The present invention is directed generally to primary or secondary,non-aqueous electrochemical cells or batteries of either active or reserve types. More particularly, the invention is directed to improvements in the high discharge rate performance of such cells including improvements in cell safety based on the use of sulfur dioxide (SO.sub.2) as the solvent in an inorganic electrolyte combination with liquid or gaseous cathode material such as the oxyhalides thionyl chloride (SOCl.sub.2) and sulfuryl chloride (SO.sub.2 Cl.sub.2) as the cathode active material. The amount of cathode active material in the electrolyte system is usually sufficient only to sustain the needed electrochemical reaction, and can be entirely consumed during normal discharge of the cell, thereby reducing the amount of highly reactive residual components to a safe level.
II. Related Art
Non-aqueous active metal cells have been in use for some time. They have enabled those skilled in the art to achieve much greater energy densities or energy to weight ratios than had been possible with other electrochemical couples. The wide range of potential uses for these cells has led to a great deal of interest in improving the performance and safety of the cells so that they may be used in a greater number of applications.
Cells of this class normally consist of a light, strongly reducing anode, normally an alkali metal such as lithium (Li) or an alkaline earth metal such as magnesium (Mg) or calcium (Ca), an aprotic, non-aqueous liquid solvent/depolarizer into which an appropriate quantity of an electrolyte salt of the anode metal has been dissolved to form a conductive electrolyte solution together, with an oxidizing agent as the cathode material. Active metal-oxyhalide systems, and particularly lithium systems, which include an electrolyte salt dissolved in an electrolyte solvent including thionyl chloride (SOCl.sub.2) or sulfuryl chloride (SO.sub.2 Cl.sub.2) are among the highest energy density cells achieved to date by any electrochemical power source. It has also been found that the discharge rate efficiency of the Li/SOCl.sub.2 or SO.sub.2 Cl.sub.2 cells can be even further increased by the addition of halogen compounds such as bromine (Br.sub.2) and interhalogen compounds such as BrCl, particularly in combination with SO.sub.2.
In the case of liquid or gaseous cathode reactions, however, the oxyhalide materials used are typically very reactive and present a cell safety problem particularly when present in an abundant quantity, as when they are also used as the electrolyte solvent/depolarizer. In these embodiments, a significant amount of the oxyhalide material is present in both the charged and discharged battery states making even the discharged cells potentially hazardous. In some of these cells SO.sub.2 may be present in smaller quantities as a dopant or additive rather than as the electrolyte solvent itself. For some time in the art, there has been a definite need to reduce the relative amounts of these high materials in the cells. There has been a need for a very high rate electrochemical cell which uses a relatively benign supporting electrolyte and cathode materials that are either close to or fully consumable as a minor constituent in the electrochemical system or consist of relatively non-hazardous materials in a solid form suitable for rechargeable or secondary cells. It would represent a great advantage if the presence of highly reactive materials could be minimized in the discharged cell without any sacrifice in cell discharge rate capability.
Accordingly, it is an object of the present invention to provide a very high discharge rate active or reserve, non-aqueous primary or secondary cell having an active metal anode and an electrolyte solvent/depolarizer/cathode combination in which the highly reactive materials are essentially fully consumed upon discharge of the cell or reduced to a level that renders the discharged cell safe.
Another object of the present invention is to achieve very high cell discharge rates in a non-aqueous inorganic electrochemical system in which highly reactive liquid or gaseous cathode reactants are not used as the principal electrolyte solvent.
A further object of the invention is the provision of a very high discharge rate electrochemical cell using an inorganic electrolyte consisting of sulfur dioxide (SO.sub.2) together with one or more salts of the anode metal in which the SO.sub.2 electrolyte system virtually does not participate in the cell reactions.
A still further object of the invention is to provide a high amperage non-aqueous inorganic cathode limited cell.
Yet another object of the invention is to provide a relatively safe, high discharge rate non-aqueous electrochemical cell capable of sustaining 100 mA/cm.sup.2 for a 10-minute or greater life.
Yet still another object of the present invention is to provide an electrochemical cell using an inorganic electrolyte consisting essentially of sulfur dioxide (SO.sub.2) as the solvent together with one or more lithium salts, in which the electrolyte serves only as an ionic conductor, in combination with a solid cathode reactant such as a lithium intercalation compound in either a primary or rechargeable electrochemical cell.
Other objects and advantages will become apparent to those skilled in the art based on the further descriptions of the invention contained herein.